Patent application title: Electronic valve system

Abstract:

An internal combustion engine comprises a number of cylinders. The
cylinders have electronically activated intake valves. Ignition coils for
the cylinders are responsive to respective ignition signals such that
charge accumulates in a coil for a cylinder when the ignition signal for
the cylinder has a first state and then the charge causes ignition for
the cylinder when the ignition signal for the cylinder changes to a
second state. In response to detecting an intake valve fault in respect
of a cylinder, the ignition signal for the cylinder is held in the first
state for a number of cycles of the internal combustion engine, and is
then switched to a second state to safely discharge the primary coil
without combustion in the cylinder.

Claims:

1. An internal combustion engine comprising:at least one cylinder having
at least one intake valve;an electronic valve actuation mechanism for
activating the at least one intake valve;at least one ignition coil
responsive to an ignition signal for the at least one cylinder such that
charge can accumulate in the coil during part of an engine cycle when the
ignition signal has a first state, which charge is used to cause ignition
for the at least one cylinder when the ignition signal for the cylinder
changes to a second state for a further part of the engine cycle; anda
control system responsive to an intake valve fault in respect of the at
least one cylinder being detected following activation of the at least
one intake valve to hold the ignition signal for the at least one
cylinder in the first state for a number of cycles of the internal
combustion engine.

2. The internal combustion engine of claim 1, wherein the control system
is operable to cause the ignition signal for the at least one cylinder to
change to the second state after the number of cycles of the internal
combustion engine approximately at a bottom dead center position of the
at least one cylinder.

3. The internal combustion engine of claim 1, wherein the control system
includes:a valve control unit operable to control the at least one intake
valve; andan engine control unit operable to generate ignition signals,
including said ignition signal for the at least one intake valve, for
controlling ignition;the valve control unit being connected by one or
more first fault signal paths to the engine control unit to pass a fault
signal to the engine control unit when an intake valve fault is detected
in respect of at least one cylinder.

4. The internal combustion engine of claim 3, wherein the engine control
unit is operable to hold the ignition signal for the at least one
cylinder in the first state for a number of cycles of the internal
combustion engine in response to receipt of said fault signal.

5. The internal combustion unit of claim 3, wherein:the at least one
cylinder comprises a plurality of cylinders organized into n sets of
cylinders;the one or more first fault signal paths comprises n first
fault signal paths, each associated with a corresponding set of the
cylinders, whereby a fault signal provided on a given one of the first
fault signal paths is representative of an intake valve fault for at
least one cylinder of a given set of the plurality of cylinders; andthe
engine control unit is operable to hold the ignition signal for each
cylinder of the given set of the plurality of cylinders in the first
state for a number of cycles of the internal combustion engine in
response to receipt of said fault signal.

6. The internal combustion engine of claim 3, wherein the engine control
unit is operable to pass the generated ignition signals, including said
ignition signal for the at least one intake valve, for controlling
ignition via a hardware interface unit, the valve control unit being
connected by one or more second fault signal paths to pass a fault signal
to the hardware interface unit when an intake valve fault is detected in
respect of at least one cylinder.

7. The internal combustion engine of claim 6, wherein the hardware
interface unit is operable to hold the ignition signal for the at least
one cylinder in the first state for a number of cycles of the internal
combustion engine in response to receipt of said fault signal.

8. The internal combustion unit of claim 6, wherein:the at least one
cylinder comprises a plurality of cylinders organized into n sets of
cylinders;the internal combustion engine further comprises n second fault
signal paths, each associated with a corresponding set of the cylinders,
whereby a fault signal provided on a given one of the second fault signal
paths is representative of an intake valve fault for at least one
cylinder of a given set of the plurality of cylinders;the hardware
interface unit is operable to hold the ignition signal for each cylinder
of the given set of the plurality of cylinders in the first state for a
number of cycles of the internal combustion engine in response to receipt
of said fault signal.

9. The internal combustion unit of claim 1, wherein the number of cycles
is a plurality of cycles.

10. An internal combustion engine comprising:at least one cylinder with at
least one electronically activated valve;a valve control unit operable to
control the electronically activated valve; andan engine control unit
operable to generate ignition signals for controlling ignition;wherein
the valve control unit is connected by one or more first fault signal
paths to the engine control unit to pass a fault signal to the engine
control unit when a valve fault is detected in respect of the at least
one cylinder.

11. A method of operating an internal combustion engine that comprises at
least one cylinder having at least one intake valve, an electronic valve
actuation mechanism for activating the at least one intake valve and at
least one ignition coil responsive to an ignition signal for the at least
one cylinder such that charge can accumulate in the coil during part of
an engine cycle when the ignition signal has a first state, which charge
is used to cause ignition for the at least one cylinder when the ignition
signal for the cylinder changes to a second state for a further part of
the engine cycle, the method comprising:detecting an intake valve fault
in respect of the at least one cylinder; andin response to detecting the
intake valve fault, holding the ignition signal for the at least one
cylinder in the first state for a number of cycles of the internal
combustion engine.

12. The method of claim 11, comprising:changing the ignition signal for
the at least one cylinder to the second state after the number of cycles
of the internal combustion engine approximately at a bottom dead center
position of the at least one cylinder.

13. The method of claim 11, wherein a valve control unit, which is
operable to control the at least one intake valve, passes a fault signal
via a signal path to an engine control unit when the intake valve fault
is detected, which engine control unit is operable to generate ignition
signals, including said ignition signal for the at least one cylinder,
for controlling ignition.

14. The method of claim 13, wherein the engine control unit holds the
ignition signal for the at least one cylinder in the first state for the
number of cycles of the internal combustion engine in response to receipt
of said fault signal.

15. The method of claim 13, wherein:the at least one cylinder of the
internal combustion engine comprises a plurality of cylinders which are
organized into n sets of cylinders; andn first fault signal paths are
provided, each associated with a corresponding set of the cylinders such
that a fault signal provided on a given first fault signal path is
representative of an intake valve fault for at least one cylinder of a
given set;the method further comprises the engine control unit holding
the ignition signal for each cylinder of the given set in the first state
for the number of cycles of the internal combustion engine in response to
receipt of said fault signal.

16. The method of claim 13, wherein the engine control unit is operable to
pass the generated ignition signals for controlling ignition via a
hardware interface unit, the valve control unit being connected by one or
more second fault signal paths to pass a fault signal to the hardware
interface unit when an intake valve fault is detected in respect of the
at least one cylinder.

17. The method of claim 16, wherein the hardware interface unit holds the
ignition signal for the at least one cylinder in the first state for the
number of cycles of the internal combustion engine in response to receipt
of said fault signal.

18. The method of claim 16, wherein:the at least one cylinder of the
internal combustion engine comprises a plurality of cylinders which are
organized into n sets of cylinders; andn second fault signal paths are
provided, each associated with a corresponding set of the cylinders,
whereby a fault signal provided on a given one of the second fault signal
paths is representative of an intake valve fault for at least one
cylinder of the set,the method further comprises the hardware interface
unit holding the ignition signal for each cylinder of the set in the
first state for the number of cycles of the internal combustion engine in
response to receipt of said fault signal.

19. The method of claim 11, wherein the number of cycles is a plurality of
cycles.

20. An internal combustion engine comprising:cylinder means, each having
intake valve means, electronic valve actuation means for activating the
intake valve means and ignition coil means responsive to an ignition
signal for a cylinder means such that charge can accumulate in the
ignition coil means during part of an engine cycle when the ignition
signal has a first state, which charge is used to cause ignition for the
cylinder means when the ignition signal for the cylinder means changes to
a second state for a further part of the engine cycle; andcontrol means
responsive to an intake valve fault in respect of a cylinder means being
detected following activation of the intake valve means thereof to hold
the ignition signal for the cylinder means in the first state for a
number of cycles of the internal combustion engine.

Description:

BACKGROUND

[0001]1. Field

[0002]Non-limiting example embodiments of the present invention relate to
the electronic valve systems for an internal combustion engine.

[0003]2. Related Art

[0004]Conventionally, internal combustion engine valve operation has been
controlled using camshafts mechanically linked to the rotation of the
engine crankshaft. With the continued aim of engine and vehicle
manufacturers to improve engines by way of reducing emissions and fuel
consumption, and to increase performance for better driveability, various
techniques to improve valve control have been employed, such as, variable
valve timing.

[0005]In order, further, to provide better control of valve actuation, it
is proposed to employ electronic valve actuation systems. Electronic
valve actuation is also sometimes known as electromagnetic valve
actuation, electromechanical valve actuation, electrical valve actuation
and the like. For consistency, the term electronic valve actuation will
be used herein. An electronic valve actuation system can be achieved by
replacing an intake camshaft with electrically activated valve actuators,
for example electromagnetic valve actuators, driven by a valve control
unit (VCU). Using information received from an engine control unit (ECU),
the VCU can drive the actuators in order to open and close the valves at
given lift and transition times in response to valve timing requests from
the ECU. The VCU can then inform the ECU of the applied valve timings.

[0006]Through such a system, independent open and closing of intake valves
at prescribed crankshaft angle timings, transition time and lift can be
based on requests from the ECU.

[0007]Non-limiting example embodiments of the present invention seek to
address the safe operation of an engine with electronic valve actuation
in the situation where an intake valve failure occurs.

SUMMARY

[0008]An embodiment of an internal combustion engine comprises a number of
cylinders. The cylinders have electronically activated intake valves.
Ignition coils for the cylinders are responsive to respective ignition
signals such that charge accumulates in a coil for a cylinder when the
ignition signal for the cylinder has a first state and then the charge
causes ignition for the cylinder when the ignition signal for the
cylinder changes to a second state. In response to detecting an intake
valve fault in respect of a cylinder, the ignition signal for the
cylinder is held in the first state for a number of cycles of the
internal combustion engine.

[0009]Holding the ignition signal in the first state prevents ignition
occurring in the cylinder, which in turn could cause ignition of fuel in
the intake manifold. Holding the signal in the first state for a number
of cycles of the engine allows fuel to dissipate via the cylinder exhaust
port(s) before the ignition signal is changed to a second state in which
ignition is permitted in the cylinder once more to safely discharge the
primary coil without combustion in the cylinder.

[0010]An embodiment of the invention can also provide an internal
combustion engine having a number of cylinders with electronically
activated intake valves, a valve control unit operable to control the
electronic valves and an engine control unit operable to generate
ignition signals for controlling ignition. The valve control unit is
connected by one or more first fault signal paths to the engine control
unit to pass a fault signal to the engine control unit when an intake
valve fault is detected in respect of at least one cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]Embodiments of the present invention will now be described by way of
example only with reference to the accompanying drawings.

[0012]FIG. 1 is a schematic block diagram of an internal combustion
engine;

[0013]FIG. 2 is a diagram representing an example relationship between
exhaust and intake valve timings and ignition timing;

[0020]FIG. 9 is a representation of a soft discharge option for a coil.

DETAILED DESCRIPTION

[0021]An embodiment of the invention can prevent unwanted ignition of fuel
in an internal combustion engine cylinder in the event of a fault in an
electronically activated intake valve following opening of the valve. In
an embodiment of the invention, in response to detection of an intake
valve fault in respect of a cylinder, the ignition signal for the
cylinder is held in the first state for a number of cycles of the
internal combustion engine to permit fuel in the cylinder to dissipate.

[0022]FIG. 1 provides a schematic overview of an electronic valve
actuation (EVA) engine system 10. The internal combustion engine 20
represented in FIG. 1 is a four cylinder gasoline engine. The engine
system is controlled by an engine control unit 40 which is connected to
various sensors and control subsystems of the engine system 10. The ECU
controls the operation of a throttle 22 at the intake side of the engine.
A manifold pressure sensor 24 in an intake manifold 32 provides control
signals to the ECU. A fuel injector 28 for each cylinder is connected to
a fuel supply line 26. A pressure regulator 30 is used to control fuel
pressure in the fuel supply line 26 and the individual injectors 28
receive control signals from the ECU to control the timed injection of
fuel. Spark plugs 34 receive ignition timing (IGT) signals from the ECU
40. In the example illustrated in FIG. 1, two electronically actuated
intake valves 36 per cylinder are provided, the electronic intake valves
being controlled by a valve control unit 38. The valve control unit 38 is
in communication with the engine control unit 40 via a dedicated bus 39.

[0023]In the example engine illustrated in FIG. 1, the exhaust valves are
controlled by a conventional camshaft 42 which is driven mechanically
from the crankshaft (not shown). The engine control unit 40 receives
signals from a camshaft sensor 44 indicating the timing of the rotation
of the camshaft 42. The engine control unit 40 also receives control
signals from a universal exhaust gas oxygen (UEGO) sensor 48 and a heated
exhaust gas oxygen (HEGO) sensor 52, either side of a catalytic converter
50, downstream of the exhaust manifold 46.

[0024]From the following description, it will be apparent that the
internal combustion engine described with reference to FIG. 1 is but one
example of an internal combustion engine in accordance with the present
invention. For example, although in FIG. 1 a conventional camshaft is
used to drive the exhaust valves for the engine, in another example of
the invention, the exhaust valves could also be implemented using
electronic valve actuators. Also, although in FIG. 1, a four cylinder
in-line engine is shown, other embodiments could include engines having
another number of cylinders and/or another configuration, for example a
V6 or V10 configuration.

[0025]FIG. 2 is a diagram illustrating the relationship between an exhaust
valve timing, an intake valve timing and the ignition spark for a cycle
of an engine such as is illustrated in FIG. 1. Thus, it can be seen that
the exhaust valve opening precedes the intake valve opening, although the
intake valve can commence opening before the exhaust valve is completely
closed. As also illustrated in FIG. 2, there is a time required to build
up charge in an ignition coil sufficient to create a spark in a spark
plug. This period, where the ignition signal is HIGH, is called the dwell
time. As spark and dwell timing is relative to crank position this is
also commonly referred to a spark and dwell angle. The spark angle is set
and the dwell time is calculated and converted into an angular value. The
dwell angle is then combined with the spark angle resulting in a location
where the ignition signal transitions from LOW to HIGH to begin dwell. In
normal operation of an internal combustion engine it is common for dwell
to have started before the intake valve has completely closed.

[0026]An example embodiment of the present invention is operable to avoid
the risk of damage to an engine or its components as a result of valve
failure in an electronic valve actuated internal combustion engine. A
problem that the present invention addresses is that, when a valve
failure is detected, it can be too late to cancel the injection of fuel
(which takes place before or during the opening of the intake valve) or
the charging of the ignition coil (the dwell time). As a result, if an
intake valve sticks in a fully or partially open position, igniting the
fuel in the cylinder with a spark plug spark could cause a backfire
through the intake manifold and cause damage to components in the intake
manifold such as, for example, the intake manifold pressure sensor, or
damage to the intake manifold itself, especially if this is made of
plastics material.

[0027]FIG. 3 provides an interrupt time line giving an example of timing
of a valve failure in an electronic valve actuated internal combustion
engine. Although in some operating conditions it may be possible to
prevent combustion through the cancellation of fuelling and ignition
requests, at higher speeds fuel injection will have already occurred and
coil charging will have started. FIG. 3 illustrates the estimated time
available for a spark interrupt signal to prevent spark in the event of a
valve closure fault. There are three stages to generating a spark
interrupt signal by the ECU 40. The valve closure fault is detected by
the VCU 36 in a detection window of 0.5 to 1 milliseconds. The valve
closure fault is then transmitted to the ECU 40. If communication of the
valve closure fault was only though standard bus communication between
the VCU 36 and the ECU 40, such as via the controller area network (CAN),
then the CAN window can be between 1 and 8 milliseconds. The ECU
interrupt time can be of the order of 1 millisecond. The lower block of
FIG. 3 represents the intake valve opening period and indicates that the
closure of the intake valve can be between 2 milliseconds (at 6500
revolutions per minute (rpm)) and 30 milliseconds (at 600 rpm) before the
spark timing. The primary coil dwell time is typically between 3.5 and 4
milliseconds. Therefore, at high engine speeds it is possible that the
ECU 40 will not be able to issue a spark interrupt signal before the
dwell time starts, and therefore the ECU 40 would be unable to prevent
ignition.

[0028]FIG. 4 is a schematic diagram of an example of an
electro-magnetically actuated valve mechanism 36. As illustrated in FIG.
4, the electro-magnetically actuated valve mechanism 36 comprises a valve
60, first and second springs 62 held in place by spring retainers 64, and
upper and lower coils 66 and 68 to cause the reciprocating motion of the
valve 60 in response to valve timing signals provided by the valve
control unit 38 shown in FIG. 1.

[0029]FIG. 5 is a schematic ignition system diagram illustrating the
components involved in generating an ignition spark through a spark plug
34. In the ignition system, a coil 70 is used to build up charge in a
primary coil 72 which is then discharged through a secondary coil 74 to
cause the spark plug 34 to generate a spark between its contacts. The
charging and then discharging of the coil 70 is controlled by an ignition
signal 84 which is provided by the engine control unit 40 illustrated in
FIG. 1. In a first phase of operation when the ignition signal 84 has a
first state (as illustrated in FIG. 5, a logical 1 state), a driver 82 is
operable to drive a power transistor 78 to cause the primary coil 72 of
the coil 70 to draw power from a battery voltage supply 76. When the
ignition signal 84 switches to a second state (as illustrated in FIG. 5,
a logical 0 state), the power transistor 78 is no longer driven by the
driver 82 and the coil 70 then discharges via the secondary coil 74.

[0030]As illustrated in FIG. 5, an ignition failure signal 92 can be
generated in response to a failure to generate ignition as detected by
the voltage bridge formed by the rectifier 80 and the current detection
resistor 86 which is connected to the amplifier 90, a second input of the
amplifier 90 being connected to ground via an impedance 88.

[0031]FIG. 6 is a schematic representation of an example configuration of
the valve control unit 38, the engine control unit 40 and the coils 70.
In the example shown in FIG. 6, optional external hardware 100 is
provided between the engine control unit 40 and the coils 90. As shown in
FIG. 6, valve failure signals are provided by the valve control unit 38
to the engine control unit 40 and to the external hardware 100 by valve
failure control lines 102, 102' and 102''. As well as the valve failure
control lines, the engine control unit 40 receives valve control unit
status signals from the valve control unit via a valve control status
line 104. The valve control unit 38 receives composite top dead center
(TDC) signals via a composite TDC line 106 from the engine control unit
40. The composite TDC signals indicate the top dead center timings for
the cylinders of the engine 20. A dedicated bus (a dedicated CAN bus) 108
provides two way communication between the engine control unit 40 and the
valve control unit 38. A crank signal line 110 is used by the engine
control unit 40 to provide crank signals indicative of crank timings to
the valve control unit 38.

[0032]The valve failure control lines can carry signals indicative of
failure of one or more of the intake valves.

[0033]In one example, a separate dedicated valve failure control line can
be provided for each cylinder of the engine to indicate the failure of an
intake valve for that cylinder.

[0034]Alternatively, the cylinders can be grouped into sets of cylinders,
with a valve failure control line being provided for a set of cylinders
to indicate the failure of an intake valve for one or more of the
cylinders of that set. For example, in the case of a V8 engine, the
engine can be divided into two banks of four cylinders, and the cylinders
can be divided into four sets, with each set comprising a corresponding
cylinder of the first bank and the second bank. Alternatively, the engine
can be divided into two sets, whereby each set represents one bank of
four cylinders. In such a case, a signal provided on a valve failure
control line is respect of a set of signals can be used initially to
cause holding of the ignition signal in the first state (e.g., a HIGH
state) for each cylinder of the set. Separate signals could then be
provided via the CAN bus to identify a particular cylinder in the set of
cylinders for which valve fault had been detected. The ignitions signal
for the other cylinders of the set of cylinders could then be permitted
to change to the second state (e.g., a LOW state) to permit ignition to
occur at an appropriate timing, while the ignition signal for the
cylinder for which a valve fault had been detected could be maintained in
the first state for the appropriate number of cycles.

[0035]Also, the valve failure signal could be encoded for transmission on
a common valve failure control line. However, in such a case, appropriate
measures are needed to decode the signals and also measures may be needed
to screen of the valve failure control line to avoid noise affecting the
encoded signals

[0036]In the example embodiment described herein, a valve failure control
signal is represented by a change from a logical 0 to a logical 1 for
ease of detection by the engine control unit 40. The valve failure
control lines 102' from the valve control unit 38 to the engine control
unit 40 form first fault signal paths. The fault signal control lines
102'' from the valve control unit 38 to the external hardware 100 form
second fault signal paths.

[0037]FIG. 7 is a flow diagram illustrating the operation of the engine
control unit in response to an electromagnetically operated valve
failure.

[0038]Step 200 represents the start of the process with the engine control
unit 40 having diagnostic input for valve failure.

[0039]The engine control unit 40 detects in step 202 whether it has
received a valve failure control signal indicative that valve failure has
been detected. The engine control unit 40 loops at this stage in the
process until valve failure has been detected.

[0040]At step 204, the engine control unit determines whether fuel has
been injected into the relevant cylinder. It is known whether fuel has
been injected or not as a result of the valve status and the point in the
timing cycle. If fuel has not been injected into the relevant cylinder,
then at step 206, the current ignition request is cancelled, and at step
208, fuel cut out for the relevant cylinder is enabled.

[0041]If, at step 204, it is determined that fuel has been injected into
the relevant cylinder, the engine control unit 40 then determines at step
210 whether the ignition coil for the relevant cylinder has been charged.
Once again, this can be determined from the point in the timing cycle for
the relevant cylinder. If the ignition coil has not been charged for the
relevant cylinder, then at step 206, the ignition request for the
relevant cylinder is cancelled, and at step 208, a fuel cut out for the
relevant cylinder is enabled.

[0042]If at step 210 it is determined that the ignition coil for the
relevant cylinder has been charged, then at step 220, the engine control
unit is operable to maintain the ignition signal high for a number of
engine revolutions, to allow fuel to be discharged into the exhaust
system.

[0043]In step 222, a fuel cut out for the relevant cylinder is enabled.

[0044]Following the aforementioned number of engine revolutions, in step
224, the coil for the relevant signal is discharged through the spark
plug at a safe time. A suitable safe time is at or around the bottom dead
center time. The process then finishes at step 226.

[0045]In the flow diagram of FIG. 7, it is indicated that the ignition
signal is maintained high for a number of engine revolutions. The number
of engine revolutions involved can be a fixed number, for example of one
or more engine revolutions. Advantageously, the ignition signal is
maintained high for a plurality of revolutions. In different examples, 2,
3, 4, 5, 6, 7, 8, 9 or 10 engine revolutions may be used. The number of
engine revolutions chosen in any particular example is a number of engine
revolutions which enables sufficient fuel to be discharged from the
exhaust system so that the mixture will be too lean at the time the coil
is subsequently discharged through the spark plug so that no ignition
will occur.

[0046]As an alternative to using a fixed number of revolutions, a number
of revolutions can be determined using feedback from the downstream
oxygen sensors 48 and 52 and/or further sensors provided downstream of
the engine 20.

[0047]FIG. 8 is illustrative of an example of the external hardware 100.
The example shown in FIG. 8 is for an eight cylinder engine whereby eight
separate coils are provided, one for each cylinder. FIG. 8 illustrates
the provision of the ignition timing signals (IGT) from the engine
control unit 40 and the provision of the valve failure signals on the
second fault control paths 120'' from the valve control unit 38. As shown
in FIG. 8, the external hardware unit 100 comprises a separate switch 150
for each of the ignition signal lines from the engine control unit. In
response to a valve failure signal on an appropriate valve failure signal
control line, the respective switch 150 is activated to switch from the
ignition timing signal lines 268 from the engine control unit to a
predetermined voltage signal 272 (in FIG. 8 a positive voltage signal) in
order to hold the ignition timing signal provided on the ignition timing
signal lines 270 to the coils 70. The provision of the external hardware
unit 100 can be advantageous for high speed or multi-cylinder engines to
ensure the latching of the ignition control signal at the high logical
value to prevent discharge from a coil for a cylinder for which a valve
failure has been detected.

[0048]To avoid a coil overheating due to being held at a high voltage,
appropriate measures can be employed, if necessary. For example, the
coils can be provided with thermal protection to shut down the coil where
the ignition signal is held high for a long time. For example, a
temperature sensing element can be provided for a coil to vary a voltage
signal with coil temperature, and when this voltage exceeds a threshold,
the coil can be caused to automatically enter a soft shut down mode to
discharge the primary coil and to protect the coil from overheating. The
soft shut down mode can be operable to discharge the primary coil
gradually by limiting the secondary voltage to a low voltage (e.g., less
than 1 kV) and thereby prevent ignition at a spark plug. FIG. 9 is a
schematic representation of such a soft shut down.

[0049]Accordingly, there has been described a system and method for
preventing the ignition of fuel in an internal combustion engine cylinder
in the event of an electromagnetically activated intake valve. By holding
an ignition signal for the cylinder in a first state for a number of
cycles of the engine, fuel in the cylinder can be permitted to dissipate,
preventing unwanted combustion of the cylinder on subsequently
discharging the coil.

[0050]Although the embodiments above have been described in considerable
detail, numerous variations and modifications will become apparent to
those skilled in the art once the above disclosure is fully appreciated.
It is intended that the following claims be interpreted to embrace all
such variations and modifications as well as their equivalents.